1. Field of the Invention
The present invention relates to printing presses, and more particularly, to a process for operating a printing press to print simultaneous print jobs wherein the first print job requires a first printing plate, sheet format, and ink zone profile, and the second print job can require a different printing plate, sheet format and ink zone profile.
2. Background Information
In the printing industry, a printer often needs to produce printing runs simultaneously in order to meet customers needs. However, such simultaneous printing jobs can therefore require a relatively quick changeover from the settings for a first print job to the settings for a second print job. Such a changeover can therefore typically require a changing of the printing plate, a changing of the paper, which can be different in size, type, and thickness, and, because of the new printing plate a changing of the ink distribution which gets carried to the printing plate, so that the appropriate amount of color is being applied by the plate. On rotary printing presses, particularly on offset rotary printing presses, it is necessary to feed a very thin and uniform ink film to a printing plate wetted by a wetting agent. For the high-viscosity printing inks normally used, a complex inking unit equipped with many rollers is generally required to produce this thin and uniform ink film. A result of the high viscosity of the inks being used and the many rollers employed in the inking unit is that it takes longer to achieve an appropriate ink distribution in the inking unit to ready the press for printing. This is especially true during a changeover from a first print job to a second print job requiring a different ink distribution from the distribution in the first job.
One process for building up an ink profile for a new print job in an inking unit of a rotary printing machine is known from the German Patent 37 07 695 C2, which corresponds to U.S. Pat. No. 5,010,820. With the solution disclosed therein, the ink available in the inking unit after a printing run is completed is returned back to the ink fountain by means of a certain number of rotations, prior to building up a new ink profile in the inking unit for a subsequent print job. Alternatively to returning the ink back to the ink fountain, this known solution suggests that the ink profile of the preceding print job be reduced while the paper is being conveyed, with the new printing plate having already been mounted on the plate cylinder. However, the result thereof is an indefinite reduction of the preceding ink profile as the new printing plate has a different ink profile and is possibly not able to remove excessive ink provided in certain zones. In this case, further machine rotations are generally necessary for reducing excessive ink from the ink zones.